1. Field of the Invention.
The invention applies to infrared detection systems and the like wherein information from one or more individual pixel detectors is sampled in time and processed into a TV type video signal.
2. Description of the Prior Art.
Due to its high sensitivity, efficiency and predictable resolution, the individual photodiode has become the preferred detection element for the retinas of infrared detection systems. Good detectors of this type were originally so difficult to fabricate and expensive that early systems used only one detector over which a two dimensional infrared image was scanned in two coordinates such as the well known "x" and "y" directions. As the technology improved it became possible to form line arrays of these detectors at reasonable costs, which need be scanned in only one direction. Such systems are now state of the art and usually consist of a vertical line array over which an image is scanned horizontally by a vibrating mirror. Two dimensional arrays are also feasible which require no scanning and hence called "staring" arrays.
The bandwidth or resolving power of these arrays is directly related to the number of detectors in the array and the response time of each detector. Current systems, however, use sampling techniques which stress simplicity and do not utilize the maximum bandwidth available. As the image is scanned horizontally across a vertical line array, the detectors are sampled vertically at a rate considerably less than twice the highest possible frequency in the output signal band to obtain a video signal. This permits an annoying distortion of the detector outputs known as signal aliasing. It results from the fact that certain high frequency components of the video signal are processed as low frequency components and abnormally increase the latters amplitude. If the higher frequencies are filtered out, this problem is reduced, but there is also a noticeable decrease in vertical resolution when the resulting signal is used to produce a visible image. In many situations, however, the aliasing is minimal and is preferable to the loss in the resolution. If the system is to be used in a wide range of applications the designer is thus put on the horns of a dilemma.